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Arrhythmogenic mechanisms in a mouse model of catecholaminergic polymorphic ventricular tachycardia.

ABSTRACT: Catecholaminergic polymorphic ventricular tachycardia (VT) is a lethal familial disease characterized by bidirectional VT, polymorphic VT, and ventricular fibrillation. Catecholaminergic polymorphic VT is caused by enhanced Ca2+ release through defective ryanodine receptor (RyR2) channels. We used epicardial and endocardial optical mapping, chemical subendocardial ablation with Lugol's solution, and patch clamping in a knockin (RyR2/RyR2(R4496C)) mouse model to investigate the arrhythmogenic mechanisms in catecholaminergic polymorphic VT. In isolated hearts, spontaneous ventricular arrhythmias occurred in 54% of 13 RyR2/RyR2(R4496C) and in 9% of 11 wild-type (P=0.03) littermates perfused with Ca2+and isoproterenol; 66% of 12 RyR2/RyR2(R4496C) and 20% of 10 wild-type hearts perfused with caffeine and epinephrine showed arrhythmias (P=0.04). Epicardial mapping showed that monomorphic VT, bidirectional VT, and polymorphic VT manifested as concentric epicardial breakthrough patterns, suggesting a focal origin in the His-Purkinje networks of either or both ventricles. Monomorphic VT was clearly unifocal, whereas bidirectional VT was bifocal. Polymorphic VT was initially multifocal but eventually became reentrant and degenerated into ventricular fibrillation. Endocardial mapping confirmed the Purkinje fiber origin of the focal arrhythmias. Chemical ablation of the right ventricular endocardial cavity with Lugol's solution induced complete right bundle branch block and converted the bidirectional VT into monomorphic VT in 4 anesthetized RyR2/RyR2(R4496C) mice. Under current clamp, single Purkinje cells from RyR2/RyR2(R4496C) mouse hearts generated delayed afterdepolarization-induced triggered activity at lower frequencies and level of adrenergic stimulation than wild-type. Overall, the data demonstrate that the His-Purkinje system is an important source of focal arrhythmias in catecholaminergic polymorphic VT.

SUBMITTER: Cerrone M

PROVIDER: S-EPMC2515360 | biostudies-literature | 2007 Nov

REPOSITORIES: biostudies-literature

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Arrhythmogenic mechanisms in a mouse model of catecholaminergic polymorphic ventricular tachycardia.

Cerrone Marina M Noujaim Sami F SF Tolkacheva Elena G EG Talkachou Arkadzi A O'Connell Ryan R Berenfeld Omer O Anumonwo Justus J Pandit Sandeep V SV Vikstrom Karen K Napolitano Carlo C Priori Silvia G SG Jalife José J

Circulation research 20070913 10

Catecholaminergic polymorphic ventricular tachycardia (VT) is a lethal familial disease characterized by bidirectional VT, polymorphic VT, and ventricular fibrillation. Catecholaminergic polymorphic VT is caused by enhanced Ca2+ release through defective ryanodine receptor (RyR2) channels. We used epicardial and endocardial optical mapping, chemical subendocardial ablation with Lugol's solution, and patch clamping in a knockin (RyR2/RyR2(R4496C)) mouse model to investigate the arrhythmogenic mec ...[more]

PMID: 17872467

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Project description:Phospholamban (PLN) is an inhibitor of cardiac sarco(endo)plasmic reticulum Ca²? ATPase. PLN knockout (PLN-KO) enhances sarcoplasmic reticulum Ca²? load and Ca²? leak. Conversely, PLN-KO accelerates Ca²? sequestration and aborts arrhythmogenic spontaneous Ca²? waves (SCWs). An important question is whether these seemingly paradoxical effects of PLN-KO exacerbate or protect against Ca²?-triggered arrhythmias.We investigate the impact of PLN-KO on SCWs, triggered activities, and stress-induced ventricular tachyarrhythmias (VTs) in a mouse model of cardiac ryanodine-receptor (RyR2)-linked catecholaminergic polymorphic VT.We generated a PLN-deficient, RyR2-mutant mouse model (PLN-/-/RyR2-R4496C+/-) by crossbreeding PLN-KO mice with catecholaminergic polymorphic VT-associated RyR2-R4496C mutant mice. Ca²? imaging and patch-clamp recording revealed cell-wide propagating SCWs and triggered activities in RyR2-R4496C+/- ventricular myocytes during sarcoplasmic reticulum Ca²? overload. PLN-KO fragmented these cell-wide SCWs into mini-waves and Ca²? sparks and suppressed the triggered activities evoked by sarcoplasmic reticulum Ca²? overload. Importantly, these effects of PLN-KO were reverted by partially inhibiting sarco(endo)plasmic reticulum Ca²? ATPase with 2,5-di-tert-butylhydroquinone. However, Bay K, caffeine, or Li? failed to convert mini-waves to cell-wide SCWs in PLN-/-/RyR2-R4496C+/- ventricular myocytes. Furthermore, ECG analysis showed that PLN-KO mice are not susceptible to stress-induced VTs. On the contrary, PLN-KO protected RyR2-R4496C mutant mice from stress-induced VTs.Our results demonstrate that despite severe sarcoplasmic reticulum Ca²? leak, PLN-KO suppresses triggered activities and stress-induced VTs in a mouse model of catecholaminergic polymorphic VT. These data suggest that breaking up cell-wide propagating SCWs by enhancing Ca²? sequestration represents an effective approach for suppressing Ca²?-triggered arrhythmias.

Project description:Most cardiac ryanodine receptor (RyR2) mutations associated with catecholaminergic polymorphic ventricular tachycardia (CPVT) are postulated to cause a distinctive form of Ca(2+) release dysfunction. Considering the spread distribution of CPVT mutations, we hypothesized that dysfunctional heterogeneity also was feasible.To determine the molecular and cellular mechanisms by which a novel RyR2-V2475F mutation associated with CPVT in humans triggers Ca(2+)-dependent arrhythmias in whole hearts and intact mice.Recombinant channels harboring CPVT-linked RyR2 mutations were functionally characterized using tritiated ryanodine binding and single-channel recordings. Homologous recombination was used to generate a knock-in mouse bearing the RyR2-V2475F mutation. Ventricular myocytes from mice heterozygous for the mutation (RyR2-V2475F(+/-)) and their wild-type littermates were Ca(2+)-imaged by confocal microscopy under conditions that mimic stress. The propensity of wild-type and RyR2-V2475F(+/-) mice to have development of arrhythmias was tested at the whole heart level and in intact animals. Recombinant RyR2-V2475F channels displayed increased cytosolic Ca(2+) activation, abnormal protein kinase A phosphorylation, and increased activation by luminal Ca(2+). The RyR2-V2475F mutation appears embryonic-lethal in homozygous mice, but heterozygous mice have no alterations at baseline. Spontaneous Ca(2+) release events were more frequent and had shorter latency in isoproterenol-stimulated cardiomyocytes from RyR2-V2475F(+/-) hearts, but their threshold was unchanged with respect to wild-type. Adrenergically triggered tachyarrhythmias were more frequent in RyR2-V2475F(+/-) mice.The mutation RyR2-V2475F is phenotypically strong among other CPVT mutations and produces heterogeneous mechanisms of RyR2 dysfunction. In living mice, this mutation appears too severe to be harbored in all RyR2 channels but remains undetected under basal conditions if expressed at relatively low levels. ?-adrenergic stimulation breaks the delicate Ca(2+) equilibrium of RyR2-V2475F(+/-) hearts and triggers life-threatening arrhythmias.

Project description:RATIONALE:Autosomal-dominant mutations in ryanodine receptor type 2 ( RYR2) are responsible for ?60% of all catecholaminergic polymorphic ventricular tachycardia. Dysfunctional RyR2 subunits trigger inappropriate calcium leak from the tetrameric channel resulting in potentially lethal ventricular tachycardia. In vivo CRISPR/Cas9-mediated gene editing is a promising strategy that could be used to eliminate the disease-causing Ryr2 allele and hence rescue catecholaminergic polymorphic ventricular tachycardia. OBJECTIVE:To determine if somatic in vivo genome editing using the CRISPR/Cas9 system delivered by adeno-associated viral (AAV) vectors could correct catecholaminergic polymorphic ventricular tachycardia arrhythmias in mice heterozygous for RyR2 mutation R176Q (R176Q/+). METHODS AND RESULTS:Guide RNAs were designed to specifically disrupt the R176Q allele in the R176Q/+ mice using the SaCas9 ( Staphylococcus aureus Cas9) genome editing system. AAV serotype 9 was used to deliver Cas9 and guide RNA to neonatal mice by single subcutaneous injection at postnatal day 10. Strikingly, none of the R176Q/+ mice treated with AAV-CRISPR developed arrhythmias, compared with 71% of R176Q/+ mice receiving control AAV serotype 9. Total Ryr2 mRNA and protein levels were significantly reduced in R176Q/+ mice, but not in wild-type littermates. Targeted deep sequencing confirmed successful and highly specific editing of the disease-causing R176Q allele. No detectable off-target mutagenesis was observed in the wild-type Ryr2 allele or the predicted putative off-target site, confirming high specificity for SaCas9 in vivo. In addition, confocal imaging revealed that gene editing normalized the enhanced Ca2+ spark frequency observed in untreated R176Q/+ mice without affecting systolic Ca2+ transients. CONCLUSIONS:AAV serotype 9-based delivery of the SaCas9 system can efficiently disrupt a disease-causing allele in cardiomyocytes in vivo. This work highlights the potential of somatic genome editing approaches for the treatment of lethal autosomal-dominant inherited cardiac disorders, such as catecholaminergic polymorphic ventricular tachycardia.

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Arrhythmogenic mechanisms in a mouse model of catecholaminergic polymorphic ventricular tachycardia.

Publications

Arrhythmogenic mechanisms in a mouse model of catecholaminergic polymorphic ventricular tachycardia.

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